Frequency Divider Circuit Errors

Frequency divider circuits can present a problem for harmonic balance. The options that prove most useful depend somewhat on whether the harmonic balance is a single-tone or multitone analysis

With single-tone analyses, convergence can be achieved by setting the method option to shooting:

.option hb.method=shooting

This shooting method for single-tone problems is a time-domain method for achieving a steady state.

Another useful option for single-tone circuits is to use transient analysis to generate the initial guess at voltages:

.option hb.initial_guess=transient

With multitone problems, successful convergence may be achieved by using the fewer_tones_transient strategy:

.option hb.initial_guess=fewer_tones_transient

The fewer_tones strategy in general calculates a single-tone solution as the initial guess for the 2-tone analysis, and proceeds to add more and more tones until the full multitone problem converges. With the fewer_tones_transient option, Nexxim uses transient analysis to generate the initial guess for the single-tone.

Convergence can also be improved by doubling or tripling the value of tstop:

.option hb.initial_guess=fewer_tones_transient.tstop=val